#define _CRT_SECURE_NO_WARNINGS 1
typedef struct ListNode LN;
struct ListNode* reverseList(struct ListNode* head) {
    LN* prev = NULL, * cur = head;
    while (cur)
    {
        LN* next = cur->next;
        cur->next = prev;
        prev = cur;
        cur = next;
    }
    return prev;
}